Organic LEDs (OLEDs) have several attractive features, such as great visual appearance, diffuse distributed light source, extremely thin or even flexible, options for transparency, mirror-like or black when off and almost complete 2D freedom in form. These properties make them ideally suited for signage applications, where luminating letters and graphic symbols of different sizes and colours are used to attract customers.
For certain application areas OLED devices have to be encapsulated in order to avoid water, moisture and/or air penetration from the environment into the device. Thin film encapsulation is one of the technologies used for avoiding such penetration into the device. The thin film encapsulation encapsulating the OLED device often comprises materials like silicon nitride, silicon carbid or aluminium oxide, and is frequently applied via a vacuum deposition process like plasma enhanced chemical vapor deposition (CVD).
In order to provide electrical connection to the OLED device, the encapsulation needs to be kept away from the contact electrodes of the OLED device. This can be achieved by using a masking process, i.e. the encapsulation is only deposited in the area of the OILED and not on the contact electrodes of the OLED.
However, the masking process is one of the main cost drivers for the deposition process of thin film encapsulation. In addition, the masking process causes yield losses due to mask handling and particle generation of the masking process.